Dialysis apparatus

In dialysis apparatus comprising an outer casing provided with two end caps respectively formed with a blood inlet and a blood outlet, a central cylindrical core located within said casing and defining an annular space therewith, said core having two end connectors which are externally accessible and respectively serve for the inlet and the outlet of a dialysis solution, a plurality of layers of capillary tubes encompassing said core within said annular space and consisting of semi-permeable hollow fibres, first flow-constraining structure arranged to cause blood to pass through the said capillary tubes in its travel between the said blood inlet and outlet, and second flow-constraining structure arranged to cause the dialysis solution to pass through said annular space along the outer surfaces of the capillary tubes in its travel between the said inlet and outlet connectors, the improvement wherein the outer surface of the said central cylindrical core dismountably carries a plurality of spacing annuli axially spaced from each other, the outer cylindrical peripheral surfaces of said annuli serving to support the radially inner layer of the said capillary tubes while the inner peripheral surfaces of said annuli are each provided with a plurality of radially inwardly extending projections defining therebetween a plurality of restricted passages for the dialysis solution to enable said solution to contact the radially innermost surfaces of said tubes along the length thereof.